This invention relates to sealing lateral connections in tubular goods. In one aspect, the invention relates to sealing lateral connections in oilfield tubular goods.
Oilfield wells and wellheads have a characteristic architecture or arrangement. Wells and wellheads have a central vertical axis of rotational symmetry. Installation & manipulation are by vertical axis displacement and/or vertical axis rotation. Cylindrical body members are typical. Concentric nesting of cylindrical body members is also typical. Installation sequence of body members progresses from larger diameter to smaller diameter. In the last analysis, a schematic representation of a wellhead arrangement would suggest stacked cups.
The present invention addresses a need arising from this characteristic arrangement. Other devices or systems may share the same characteristic arrangement and might share in the benefit of the present invention.
The upper end of the wellhead system is closed by any one of a number of devices, providing control of fluid flow and pressure entering and/or leaving the well. This closure device is typically installed vertically, as a cap attached to the end of one of the wellhead's concentric body cylinders, and sealing fluid pressure at the upper end of one or more of the body cylinders.
A basic function of a wellhead system is to provide for fluid flow into the well and/or out of the well. The outer end of the required pathway(s) is outside of the outermost well barrier. The inner end of the pathway(s) is either the wellbore or one of the annular spaces between the concentric tubes or tubular bodies.
The basic flow in the pathway(s) is that of produced (or injected) fluids. This may include flow of well fluids which enter (or are introduced into) the annular spaces in the system.
A second, but critical flow is that of pressurized fluids used to control or operate devices in the well, such as downhole valves.
A less obvious need is the communication of non-fluid flow. Here a fluid-tight pathway is used to allow passage of a cable, for electrical or even optical signals. Here a fluid-tight path is required to exclude fluid rather than to contain it.
Examples of wellhead pathway connections are many. These include a concentric vertical stab using a conventional single completion tubing bonnet (wing outlet above master valve); an eccentric vertical stab using a dual, orienting tubing hanger and bonnet; a storm choke or SCSSV control stab; a control system such as the Knerr et al control stab ring, the Seehausen control connector, or NL control connections. Also included are these: concentric control line galleries on a side valve tree tubing hanger; an eccentric side penetrator (such as the Blizzard BOP tree control connector); or the Vetco shearable stinger.
Vertical connection of pathways is the most basic, typical approach. Its main advantage is that it relates well to the sequential "stack-up" of the system components. Also, it agrees with the installation motion, vertical displacement. Its disadvantages include these: that it requires rotational orientation around the well axis if the path is not concentric; it adds vertical stack-up height, and component subassemblies, to accommodate connection(s) and seals; it limits the number and size of connections into an annulus by its boundary diameters.
Horizontal (radial) connection of pathways requires no rotational orientation to the well axis if gallery seals are used. However, if a horizontal connection (penetrator) crosses over a diameter interface between two concentric bodies of the wellhead assembly, it "locks" those bodies together and vertical displacement or removal of the inner from the outer body is prevented. Traditional "stab" connections (male/female) embody this disadvantage when configured in the horizontal orientation.
At the top of a completed wellhead system there is a tubing hanger installed in a tubing spool (or tubing bowl). Above this a bonnet provides a transition and interface to the bottom connection of a Christmas tree.
In an arrangement of tubing hanger and tubing spool, regardless of which configuration, there are basic boundary penetration requirements. All may be viewed as candidates for adaptation to horizontal penetration/connection. The boundary penetrations are these:
1. pressurized control fluid; this operates downhole valves, or other devices; PA1 2. annulus fluid (casing tubing annulus); this may be at pressure or not, flowing or not, and may be "inbound" or "outbound"; PA1 3. production fluid; again, this may be at pressure or not, flowing or not, and may be "inbound" or "outbound"; PA1 4. electric current; this may be low voltage and current, transmitting a signal to/from a downhole sensor or device. Alternatively this may be a high voltage and current transmitting power to a downhole device (usually a pump). PA1 1. reduced interflow risk PA1 2. multiple radial connections on the same horizontal plane, saving stack-up height PA1 3. simplified bonnet/tree cap PA1 4. readier vertical access to the inner body (tubing hanger) PA1 5. reduced risk of damage to seal surfaces in the spool, vertical scratching incurred in installation/removal of the inner body. PA1 1. failure to retract a stab may result in the need to shear out the stab body PA1 2. a push/pull mechanism is built into the tree spool; this adds complexity and failure modes to the item you wish to leave undisturbed. PA1 1. The shear seal interface is beneficially planar while the interface here is cylindrical. Use of the small radial displacement allows installation of the inner (hangar) body with an unobstructed cylindrical space. PA1 2. Potential for damage to seal surfaces on installation and removal is reduced. PA1 3. Positive energizing of the face seal is achieved. PA1 4. Use of a metal seal is facilitated, because of the actuation.
In typical tubing hanger arrangements penetrations for pressurized fluid, including control fluid, have used a variety of designs. There are vertical, eccentric stabs (bonnet to hanger), as well as vertical, concentric connections (gallery seals, bonnet to hanger). Vertical connections may require orientation, and utilize space inefficiently. Gallery seals, when used, add problems of leak paths and interflow.
Recently, horizontal fluid connections with push/pull stab connections have been proposed. In these systems the hanger, including its side facing female receptacles, is rotationally oriented to the spool. The spool carries side facing male stabs, moved in/out radially by independent actuators (generally, hydraulic with/without spring bias). The system requires orientation of the hanger in the spool.
Furthermore, as noted above, the horizontal stab system has as a potential failure mode the locking of the hanger in the spool if the stab fails to retract. In the commercial system it has been proposed to deal with this failure mode by providing a weak point in the stab, corresponding to the point at which it bridges the cylindrical interface diameter between the hanger and the spool. In this way, failure to retract the stab can be overcome by forcibly withdrawing the hanger from the spool. In this action the stab will be sheared at its weak point. This allows for emergency recovery of the hanger, but leaves open the question of repairing the stab.
Typical electrical connections/penetrations have used vertical male/female stabs, requiring orientation and alignment. Reliability of these items is a concern, and access to either half of the connection is limited, limiting effective maintenance and repair.